//生成随机字符串
export default function(len=30) {
    const $chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
    const maxPost = $chars.length;
    let str = '';
    for(let i=0;i<len;i++) {
        str+=$chars.charAt(Math.floor(Math.random()*maxPos))
    }
    return str;
}